Respect the Dark Jedi, Hetton:

Power

According to the The Complete Star Wars Encyclopedia Hetton had a "Strong" connection to the dark side.

Credit to EmperorDMB

Hetton "Radiated" with the power of the dark side.

"Although he was not conventionally attractive or physically imposing, there was an undeniable air of importance about him. Zannah suspected it was a natural confidence born of wealth and privilege, but as she was marched down the red carpet toward him, she realized it was something far more impressive: Hetton radiated with the power of the dark side!"

Darth Bane: Rule of Two.

Zannah could tell that Hetton had been trained in the dark side and that his power was to refined to be merely inherent.

"You and Paak seem to have survived somehow," Zannah remarked, letting the unspoken accusation hang in the air as she continued her subtle probing of Hetton.

His power didn't have the raw, untamed feel of one who had never been trained. Was it possible he'd once had a tutor or mentor? Had someone knowledgeable in the Force taught him the ways of the dark side, then abandoned him to follow Kaan? Or was there some other explanation?

Darth Bane: Rule of Two.

Zannah could feel hetton gathering the power of the dark side.

"What were you thinking?" he demanded with a sudden shout that made both Paak and Cyndra jump. Zannah could feel the air crackle as the small man called upon the Force, gathering the energies of the dark side.

Darth Bane: Rule of Two.

Hetton's power was "Undeniable".

His power was undeniable, yet as she felt it building she was confident his abilities would be no match for hers. "Hetton, wait!" Paak shouted, sensing the peril they were in. "We've got something for you."

Darth Bane: Rule of Two.

Hetton's power at a young age, was enough that the servants who watched over Hetton were aware of his force ability.

"My father died when I was only an infant," Hetton said, his voice low enough that Zannah had to strain to hear it over the clacking of their footsteps on the polished marble floor. "Burdened with the responsibilities of being the head of our house, my mother left it to the servants to raise me. They knew of my special gifts for many years before word of it ever reached my mother's ear."

Darth Bane: Rule of Two.

Hetton was able to gather 8 Umbaren shadow assassins to his cause. it can be potentially implied that Hetton is superior to then at least individually.

Under the separatist banner, I drew those individuals with unique skills and talents into my service. We were united in our hatred of the Republic and the Jedi, yet I was still wary of revealing my true purpose: the resurrection of the Sith!

...

"I have more resources at my disposal than you might imagine," he said, raising his hand and snapping his fingers.

Two of his red-cloaked guards appeared beside him, seeming to materialized out of thin air. Zannah let her hand drop to her lightsaber, wondering if she had been lured into a trap. She couldn't figure out where the guards had suddenly come from; even if they were somehow cloaked, she should have been able to sense their presence through the Force.

The guards made no move to attack her, however, and a second later she relaxed once more and looked questioningly at Hetton.

"As I told you before, I have recruited a number of individuals with unique and specialized talents to my side," he explained. "Included among them are eight former students of the Sith Academy on Umbara."

Through Bane, Zannah knew those students sent to Umbara were trained in stealth and assassination, learning to use the Force to mask their presence from all manner of detection. That was why she had been unable to sense them in the room.

"Should you accept me as your apprentice, my guards will swear fealty to you as well," Hetton told her. "You will have a squad of eight unstoppable, undetectable killers at your command."

Darth Bane: Rule of Two.

Zannah attempts to judge who would be more likely to win in a battle, Hetton and his assassins, or Bane. Ultimately she can't decide which outcome is more likely. This speaks highly of both the ability of the shadow assassins and the power of Hetton himself.

In her mind Zannah weighed all she knew of Darth Bane's strength and power against Hetton and his eight Shadow Assassins, trying to determine which side had the upper hand. In the end she couldn't accurately predict who would survive such an encounter, but she decided she wanted to find out.

Darth Bane: Rule of Two.

Knowledge

Hetton had a vast collection of sith manuscripts and artifacts.

She and Hetton were alone now. After her performance in the throne room, he had insisted on bringing her to see his vast collection of Sith manuscripts and artifacts, located in his inner sanctum on the far side of the great mansion.

Darth Bane: Rule of Two.

Hetton was trained for a period of time by a bounty hunter named Gula whom had both a connection to the force, and a understanding of basic techniques in order to use it. This includes telekinesis.

"Master was a title he never deserved," Hetton replied with just a hint of bitterness. "He was nothing but a bounty hunter and assassin who had the good fortune to be born with the ability to touch the Force. Over the years he had gleaned a simple understanding of the most basic techniques to access his power, allowing him to levitate small objects and perform other similar tricks,

Darth Bane: Rule of Two.

Hetton had a room full of ancient manuscripts and sith treasures.

The room was part library, part museum. Shelves of ancient manuscripts and scrolls, and endless lines of old datatapes lined the walls, and there was a data terminal and large viewscreen in one corner. Several long glass display cases ran lengthwise down the center of the room, displaying the collection of Sith treasures Hetton had spent the past three decades acquiring: strange glowing amulets, small jewel-encrusted daggers, a variety of unusual stones and crystals, and the handles of at least a dozen different lightsabers.

Darth Bane: Rule of Two.

Hetton Possessed artifacts that have the remnant of darkside power still apart of them, these article at one point however contained "Incredible power"

They walked slowly along the length of the display cases, Zannah splitting her attention between Hetton's words and the intriguing array of Sith artifacts. She could still feel faint remnants of dark side energy clinging to them: fading memories of the incredible power they once contained.

Darth Bane: Rule of Two.

The treasures Hetton had rivaled those of Set Harth, As well as Hetton being stated to be "Obsessed" with the darkside.

Zannah had seen collections like this before. Ten years ago Hetton, a Force-sensitive Serrenian noble obsessed with the dark side, had shown her a similar trove of Sith artifacts:an offering he had hoped would convince Zannah to take him on as her apprentice despite his advanced age.

Darth Bane: Dynasty of Evil.

Credit to EmperorDMB

The knowledge Hetton gained allowed him to "Quickly Surpass" Gula.

"The knowledge here allowed me to quickly surpass Gula. Once my mother realized he was no longer of any use to us, she had him killed."

Darth Bane: Rule of Two.

Telekinesis

Hetton unlocks a door with the force, presumably through telekinesis.

They had reached another set of large double doors, though these were sealed and locked from the other side. Her host reached out and placed his palm on the surface, then closed his eyes. Zannah felt the soft whisper of the Force; then the lock clicked and the door swung open to reveal Hetton's inner sanctum.

Darth Bane: Rule of Two.

Force Lightning

Hetton unleashes a bolt of force lightning at Darth Bane, being deflected with the blade of Bane's lightsaber.

While the four remaining assassins regained their feet, Bane wheeled back to their leader. Wisely, the man in black had stopped his own charge and was gathering the Force. As Bane stepped toward him the man unleashed it in a single long, thin bolt of indigo lightning. Bane caught the blast with his lightsaber, the blade absorbing the energy.

Darth Bane: Rule of Two.

Speed

Hetton moves fast enough to avoid a blast of Bane's lightning.

In retaliation he struck back with lightning of his own- a storm of a dozen bolts arcing in toward his target from all angles.

The man leapt high in the air, flipping backward to avoid the deadly electrical conflagration. He landed on his feet ten meters away, a small, smoking crater marking the spot where he had been standing only an instant before.

Darth Bane: Rule of Two.

Combative Ability

Hetton killed his former teacher Gula, a bounty hunter and force sensitive.

"A necessary death" Zannah said with a nod, realizing that Bane probably would have done the same thing. Then, hit with a sudden flash of insight, she said, "You were the one who killed him, weren't you?"

Hetton smiled at her. "You are as perceptive as you are powerful. When the order came down from my mother, I was more than happy to comply. Gula had become a burden and an impediment to my own research into the ways of the dark side."

Darth Bane: Rule of Two.

"Age has little relevance in matters of the Force."

-Hetton, Darth Bane: Rule of Two.